How accurate is the racetech spring rate calculator?

[Costa Rican YZ450F]

How accurate is the racetech spring rate calculator? Here is one for the suspension gurus, I weight 175-179lbs it says I should go with 5.35kg/mm rear spring instead of the 4.7 stock, I’m using 102-100 mm race sag and my static is 25mmish. Will this spring make any handling improvement even though I’m at those numbers?

Thanks in advance,

Carlos

[arnego2]

What kind of riding do you do?

[meinmoto]

I'd say your close enough in sag numbers to just leave it if you dont need to spend the dough. Exactly what kind of handling differences are you trying to achieve? Race tech's calc is pretty good, it asks you what riding you do all the way down to if you have an oversize tank or not. Also make sure your being honest when it asks what your level of riding your at. Otherwise it may suggest an overly stiff setup. I've always trusted thier calc and know many riders who do the same and love the results. Also, your shock spring is the infamous titanium one and the race tech spring is probably steel. Ive heard those ti shock springs are around 600 bucks from yamaha.

[Costa Rican YZ450F]

Sorry guys, I ride only mx, amateur level I get out at least 1 to 2 times minimum per week, I don't have any problems with the rear, I just need to order everything I need for the bike since I live overseas and was going to make an order and was wondering since I'm ordering should I get the spring, whats the difference between the ti and steel? which is better for mx?

Thank again

[meinmoto]

Spring rate is what matters. The Ti spring is just a bonus because its lighter. So if you can make it work, keep it. Based on your sag numbers your close. Its your call on where to spend your money.

[rjpjnk]

How accurate is the racetech spring rate calculator? Here is one for the suspension gurus, I weight 175-179lbs it says I should go with 5.35kg/mm rear spring instead of the 4.7 stock, I’m using 102-100 mm race sag and my static is 25mmish. Will this spring make any handling improvement even though I’m at those numbers?

Thanks in advance,

Carlos

The 4.7 is the stock spring for the 125, but your signature says YZ250. The stock spring on the 250 is 4.9.

Which bike do you have, and are you sure you have the original spring?

EDIT: Either way, you current sag numbers look ok, but on the heavy side for that spring.

Edited April 17, 2013 by rjpjnk

[meinmoto]

The 4.7 is the stock spring for the 125, but your signature says YZ250. The stock spring on the 250 is 4.9.

Which bike do you have, and are you sure you have the original spring?

I was going by his sig too lol...hope its the 250. 4.9 to 5.3 isnt near as bad as 4.7 to 5.3... like his sag measurements show, hes close.

[JRod4928]

I'm wondering if your spring is the stock spring as well.. Is it a light silver color? If so, that's a titanium spring and probably the stock 4.9 Ti spring. If not, it's probably a lighter steel spring.

Either that or your linkage bearings needs greased/replaced and the drag from the linkage is giving you inaccurate readings.

Are you pushing down on the rear end and letting it rebound when you take the sag readings? Or are you just letting the bike drop under its own weight?

[RCannon]

The racetech calculator is almost worthless. Few bikes are shown with the correct stock spring rate. I also believe that many of the recommended rates may be based on using their other components.

I've not owned one motorcycle, dirt or street, where the race tech info was accurate...

[Costa Rican YZ450F]

The bike is an 09' yz250 and my spring is blackish pretty sure its the original, how can you tell its on the heavy side? Heavy as I'm to heavy for it? what's a good static sag? I though it was 4.7 like the racetech site says. Just regreased my linkage 2 weeks ago its good to go :-) What I notice is that there is a good distance that the spring is compressed down from the top of the shock, that's why I was thinking I new spring. so if its 4.9 a 5.3 wont make much of a difference?

Edited April 17, 2013 by Costa Rican YZ250

[JRod4928]

The bike is an 09' yz250 and my spring is blackish pretty sure its the original, how can you tell its on the heavy side? Heavy as I'm to heavy for it? I though it was 4.7 like the racetech site says. Just regreased my linkage 2 weeks ago its good to go :-) What I notice is that there is a good distance that the spring is compressed down from the top of the shock, that's why I was thinking I new spring. so if its 4.9 a 5.2 wont make much of a difference?

Can you post a photo of it? If it's black, I'm pretty sure it's not stock, it should be the titanium spring. They used the titanium spring on the 2009 YZ 250, says so on MXA's review, here http://www.motocrossactionmag.com/Main/News/2009-Yamaha-YZ250-TwoStroke-Suspension-Settings-Je-6203.aspx

This is what the spring should look like if it's titanium. http://www.ebay.com/itm/Yamaha-Kayaba-4-7kg-mmTITANIUM-Shock-Spring-YZ-125-250-250F-450F-NEW-PRICE-DROP-/130863337301?pt=Motorcycles_Parts_Accessories&hash=item1e78100f55&vxp=mtr#ht_426wt_1129

There are a few ways to tell the spring's springrate. It's hard to tell the springrate by just looking at it. 1) Put it on a test machine to measure it's spring rate, 2) Find the paint blot on the spring and match the color with the corresponding code given by the spring's manufacturer, or 3) If the suspension was previously worked on by a suspension shop, call them and ask what was installed. Or call the previous owner.

If your spring is black, it's probably an aftermarket steel spring, not the stock titanium spring. If you remove it, it'll be heavy.

From what you're telling me, it sounds like someone put a softer spring in, but I can't be 100% sure without seeing it myself. I'd call a suspension shop and see what springrate they recommend for your height/weight/ability/bike.

[Costa Rican YZ450F]

Yeah for sure this is it http://www.oemdirtbikeparts.com/rear-shock-2000-2001-2002-2003-2004-2005-2006-2007-p/yz250-rear-suspension.htm

How can you tell its a light spring for me?

[JRod4928]

here's a good explanation and walkthrough. basically, if you set your rider sag to 100 and your other sag is less than 30, you need stiffer springs, if it's more than 40, you need softer springs.

http://motocrossactionmag.com/Main/News/MX-EDUCATION-HOW-TO-SELECT-THE-CORRECT-REAR-SHOCK-2413.aspx

[JRod4928]

I must say that these are all guidelines, not rules. So if you set your sag to 105/30 instead of 100/25, and it's performing well for you, then why mess with it? These are just suggestions to get you in the ballpark, it's all fine tuning from there. The idea is that with sag set to 100/35 (+/- a few millimeters), your shock will be operating within the stroke that it was designed for - which will give you optimum performance.

I had a 4.2 spring on my bike (rider was 115 lbs), and I set the sag for my weight (165 lbs) and it came out at 100/22...... Switched to 4.9 and sag is now 100/32 or so. The 4.9 was suggested to me by a reputable shop, and I believe, by racetech's spring calculator.

?

Edited April 17, 2013 by JRod4928

[Costa Rican YZ450F]

I must say that these are all guidelines, not rules. So if you set your sag to 105/30 instead of 100/25, and it's performing well for you, then why mess with it? These are just suggestions to get you in the ballpark, it's all fine tuning from there. The idea is that with sag set to 100/35 (+/- a few millimeters), your shock will be operating within the stroke that it was designed for - which will give you optimum performance.

I had a 4.2 spring on my bike (rider was 115 lbs), and I set the sag for my weight (165 lbs) and it came out at 100/22...... Switched to 4.9 and sag is now 100/32 or so. The 4.9 was suggested to me by a reputable shop, and I believe, by racetech's spring calculator.

?

Last question I'm better going with the 5.4 then the 5.2 spring rate? the calculator says 5.36; and when I get home I will double check my numbers,

[BeauGt]

Race Tech bases their spring rates off the valving that they use. Usually their spring rates are soft if you are basing it off OEM valving.

[JRod4928]

I'd contact factory connection, or a local suspension shop and see what their opinion is. I'm not sure which is best and I'd hate to lead you the wrong way.

[rjpjnk]

The bike is an 09' yz250 and my spring is blackish pretty sure its the original, how can you tell its on the heavy side? Heavy as I'm to heavy for it? what's a good static sag? I though it was 4.7 like the racetech site says. Just regreased my linkage 2 weeks ago its good to go :-) What I notice is that there is a good distance that the spring is compressed down from the top of the shock, that's why I was thinking I new spring. so if its 4.9 a 5.3 wont make much of a difference?

You can tell if it's titanium if a magnet does not stick to it.

The OEM titanium springs have a color coded dot painted on the last coil indicating the rate (this is described in the service manual) 4.7 has a red dot, 4.9 black, and 5.1 blue. There can be 1, 2, or 3 of these colored lines indicating length, but the rates are still the same. Here is an example of the color dot on ebay. This spring has a red dot on the last coil indicating it is a 4.7 (not 5.1 as claimed by seller).

http://www.ebay.com/itm/2006-YAMAHA-5-1kg-TITANIUM-SHOCK-SPRING-YZ-WR-125-250-250F-426F-450F-1996-2013-/360624725542?pt=Motorcycles_Parts_Accessories&hash=item53f6e89e26&vxp=mtr

The reason I said you are on the heavy side for that spring is based on the sag numbers. As you increase the preload on the spring by tightening the adjuster rings on top this raises the bike up higher (both static and race sag decrease). You can make even a very light spring give you 100mm race sag if you crank it down tight enough, but you will need an excessive amount of preload to do this. From what I understand, these springs have a sweet spot at around 3-7 mm of preload. Any more than this and the spring starts to feel too bouncy and becomes less linear towards full compression. Since it is difficult to measure preload while the spring is on the bike we estimate preload using static sag instead. As others have stated, you typically want to have about 25-40 mm of static sag left when you have reached your race sag target. The fact that you have only 25 is what makes me say you are on the extreme end of this spring's operational range (i.e., you are slightly too heavy for it).

The preload is the diference in spring length from it full uncompressed length to the length as installed on the bike with no weight on it. i.e., it is a function only of the adjustment rings. At 175 you are about the perfect target weight for that bike and the OEM spring should be just right, but since you mentioned your spring appeared to be adjusted way down from the top it made me wonder if it was in fact a lighter spring that someone had cranked down in order to raise the race sag, then you mentioned 4.7, which would be a lighter spring.

I believe you will be fine riding that spring, but may want to back your race sag down to 105 (probably leaving you about 30 static). If you want to get closer to "perfect" you could try 1 or 2 spring sized heavier.

Can you tell me the color dot on the present spring? You can usually see it while on the bike with a small flashlight.

[JRod4928]

I believe most of that was covered ?

[rjpjnk]

I believe most of that was covered ?

Yeah, I know, I just love talking about this stuff. ? You nailed it above already.